This invention relates mainly to a light-emitting diode (LED) device and, more in particular, to such a device suited to be used as a light source for an illuminator with a light-emitting surface of a so-called back lighting type.
Liquid crystal panel displays are commonly used as a display device for a compact electronic apparatus because they can not only display many different kinds of patterns with small power but also can be made thin. These liquid crystal panel displays do not emit any light themselves and are often used in combination with an illuminator having a light-emitting surface of the back lighting type placed behind it so as to improve the visibility.
As shown in FIGS. 20 and 21, an illuminator 10 of this kind having a light-emitting surface generally comprises a light-conducting transparent or translucent rectangular plate 11 with a uniform thickness made of a resin material, and LED devices 12 serving as a light source are disposed along its mutually opposite shorter edges.
As shown in FIGS. 22 and 23, each LED device 12 comprises a horizontally elongated rectangular box-shaped reflector case 13 containing a specified number (two, according to this example) of LED chips 14 forming light source units 15, external terminal lead lines 16 extending downward from the bottom surfaces of these light source units 15. The height L.sub.1 of the reflector case 13 is less than the thickness of the light-conducting plate 11, and its length L.sub.2 may be suitably determined with respect to the planar dimensions of the light-conducting plate 11. The front surface of the reflector case 13 is open and its sloped inner walls serve as reflecting surfaces.
The two LED chips 14 of each LED device 12 are electrically connected to each other in series. As can be seen in FIGS. 23 and 24, there are three elongated terminal plates (first, second and third) 17, 18 and 19 disposed in series at the bottom of the reflector case 13. One of the LED chips 14 is bonded to an end part of IS the first terminal plate 17 and is connected to one end part of the second terminal plate 18 by wire bonding, and the other LED chip 14 is bonded to the other end part of the second terminal plate 18 and is connected to one end part of the third terminal plate 19 by wire bonding. The end parts of the first and third terminal plates 17 and 19 distal from the second terminal plate 18 are extended downward, serving as the external terminal lead lines 16. The bonding wires and the LED chips 14 are sealed inside the reflector case 13 by means of a transparent or translucent protective resin material.
As best shown in FIG. 21, the light-conducting plate 11 is provided with concave grooves 20 for containing therein the light source units 15 of the LED devices 12. Throughholes 21 are provided at the bottom of the grooves 20 for passing the external terminal lead lines 16 therethrough.
When the reflector case 13 is produced by a resin molding method, the three terminal plates 17, 18 and 19 are inserted together, but since they are inserted so as to be mutually separated longitudinally, as shown in FIG. 23, problems as described below sometimes occur when the LED devices 14 are installed inside the light-conducting plate 11.
When a LED device 12 is installed in the light-conducting plate 11 by using a suitable mounter, the reflector case 13 is usually held at a middle part in the longitudinal direction to be inserted into a specified groove 20. Since the terminal lead lines 16 at both end parts of the reflector case 13 experience some resistance as they are passed through the throughholes 21, shearing forces appear inside the reflector case 13 as shown by the arrows in FIG. 24. Such forces are concentrated where the terminal plates 17, 18 and 19 are separated with a gap in between, say, along the line A in FIG. 24. This makes it likely to generate cracks along such lines. Since it is considered desirable to make the light-conducting plate 11 as thin as possible, and the height of the reflector case 13 is less than this thickness, a situation as described above is very likely to occur. Since a bonding wire crosses the line A, such a crack, as it becomes larger across the line A, may adversely affect the electrical connection by the bonding wire.